In electrical and electronic circuit engineering, a transformer is a versatile and ubiquitous component that accomplishes impedance level transformation between its primary and secondary windings through magnetic coupling, while providing direct current (DC) isolation between the primary and secondary windings. These properties are useful today in the field of IC design, and especially for radio frequency (RF) IC design, because inductive components such as spiral coils functioning as primary and secondary windings can be fabricated with good performance characteristics using known semiconductor fabrication techniques.
FIG. 1 illustrates an example geometry of a transformer 100 integrated on an IC. An integrated spiral transformer can be employed to transform impedance levels between different parts of an IC, convert signals from balanced (differential) to single-ended format, or interface chip circuitry to off-chip devices, circuits or fixtures. For instance, an integrated transformer can be employed to interface low impedance (e.g. few ohms) output of an integrated complementary metal oxide silicon (CMOS) power amplifier (PA) through the output pad of the IC and to an external 50-ohm system. Some of these applications are described in detail, for example, in the book “RF Microelectronics” by Behzad Razavi.
What is needed then are methods and systems for improving and/or simplifying the design of components such as integrated spiral transformers for use in ICs fabricated using modern semiconductor fabrication techniques that take into account the different functionality of the designed-for transformers and the interaction of such transformers with other components of an IC.